The invention relates to the field of fine chemicals. More precisely, the invention relates to a process for the manufacture of a non-oily emollient.
Emollients are widely used in the cosmetic and pharmaceutical industries to render dry skin soft and to improve its elasticity. The term emollient generally refers to the set of perceptions conveyed by the senses of touch and sight. Perceptions evoked by touch are softness, elasticity and smoothness. Perceptions evoked by sight are shininess and dullness.
A considerable number of emollients are offered by suppliers of cosmetic starting materials. These emollients differ from each other in terms of their chemistry, as well as in terms of the result of two factors: emollience on application and residual emollience. There are therefore emollients with a protective effect, others with a highly oily effect, while some give the impression of dryness and others still have an astringent effect.
The vast majority of emollients are characterised by the presence of fatty acids with fairly long carbon chains, either linear or branched. These fatty acids are themselves combined, in the form of esters, with alcohols with more or less long carbon chains which are also linear or branched. It is these esters and fatty acids which constitute the basis of the emollient effect. Generally, two groups of esters are considered to make up this category of emollient: those of a completely natural origin and those of synthetic origin, synthesis meaning esterification of the fatty acid by an alcohol. Synthetic esters are usually manufactured from saturated fatty acids. This confers great stability on them with regard to oxidation but eliminates the possibility of their being involved in any biosynthetic processes in the epidermis. It is well-established that polyunsaturated fatty acids (linoleic and linolenic acid), called essential fatty acids, can be transformed by the enzymes of the epidermis into other polyunsaturated fatty acids which, amongst other effects, are likely to limit the loss of transepidermal moisture. This limiting effect on loss of moisture provides skin emollience and it is this emollient effect that is sought after in esters of natural origin, such as those found in plant oils and fats, marine oils and some animal fatty materials.
All these fatty materials consist of a mixture of esters that are triglycerides or triesters of glycerol and fatty acids. It is the properties of the fatty acids found in these esters which give the resultant fatty material its consistency. Therefore the richer these fatty materials are in saturated fatty acids, the greater their consistency to the point where fairly solid fats or butters are obtained at 20xc2x0 C. Totally solid products can actually be obtained at this temperature with completely hydrogenated fats. Conversely, the lower the content in unsaturated fatty acids (mono- or poly-), the more likely the fat is to be totally fluid at 20xc2x0 C.
This is true of vegetable oils which are characterised by a composition in which overall content in unsaturated fatty acids is often greater than 85%. The liquid consistency of oils is one advantage in terms of an emollient effect. To this fluid consistency is added the effect of essential fatty acids such as linoleic acid, always present in vegetable oils in varying proportions as a function of the botanical origin of oleaginous species from which they originate. As mentioned earlier, transformation of linoleic acid into other unsaturated fatty acids via a biosynthetic process leads to a significant moisturizing effect which contributes to maintaining the epidermis in a good state of emollience. Finally, the important biological role played by the unsaponifiable compounds present, such as squalene, carotene, triterpenic alcohols and phytosterols, have to be taken into consideration with vegetable oils. These oils can, however, be completely hydrogenated to give emollient fatty materials, devoid of biological activity but oxidatively very stable, and which have the required consistency for some creams.
While all these advantages are well known, vegetable oils and fatty materials in general nonetheless have the serious disadvantage of being oily to the touch after application to the skin because of their low rate of skin penetration. Generally speaking, the rate of percutaneous penetration of a molecule is inversely proportional to its molecular weight. This rate is relatively high for a molecular weight of 400 Dalton but above this molecular weight, the rate of penetration decreases considerably. However, the molecular weight of triglycerides in vegetable oils is around 870 Dalton, much higher than the limit of 400 Dalton. It is therefore clear that vegetable oils, such as those used in cosmetic and pharmaceutical formulations, can give the impression of being oily as a result of triglycerides which only penetrate the skin very slowly.
The problem faced is therefore to find a process for manufacturing emollients where the molecular weight of the principal compounds is below about 600, preferably around 500, and still more preferably below about 450 Dalton, in order to obtain vegetable oil and fatty materials based emollient preparations that are not oily to the touch. The second objective consists in transforming vegetable oils or fatty materials in general and purifying the product obtained under conditions such that the intactness of their fatty acids and insaponifiable matter is not lost so that all the properties of fatty materials can be exploited without the inconvenience of their being oily.
This problem is resolved by the process of the invention which is comprised of the following steps:
a) interesterification of the triglycerides contained in a fatty material, preferably of vegetable origin, by a primary alcohol, preferably of plant origin, in the presence of a catalyst;
b) elimination of the catalyst;
c) distillation of the residual alcohol, preferably in the presence of a bleaching agent, followed by elimination of the bleaching agent;
d1) either frigelisation of the preferably bleached residue such that residual glycerides are at least partially crystallized, followed by elimination, especially by filtration, of said crystallized residual glycerides;
d2) or hydrogenation of the residue, preferably bleached.
In step d1), said residual glycerides are mono-, di- or triglycerides resulting from esterification by said primary alcohol in step a). Their elimination results in products that are completely liquid at the frigelisation temperature, notably at room temperature, preferably at a temperature of at least 15xc2x0 C.
In step d2), hydrogenation of the residue leads to the formation of products with higher melting points at room temperature, generally melting points between a temperature of 25xc2x0 C. and 80xc2x0 C., depending on the molecular weight of the products.
In the sense of this invention, xe2x80x9cfatty materialxe2x80x9d refers to a refined or crude vegetable oil or fat, possibly hydrogenated, a refined or crude marine oil, possibly hydrogenated, or a refined or crude animal fat, possibly hydrogenated, or a refined or crude anhydrous dairy fat, possibly hydrogenated.
The alcohol use in the interesterification step can be chosen from the C1-C22 alcanols, C3-C22 alcenols or C3-C22 branched alcohols. These branched alcohols are alcohols likely to carry C1-C8 alkyl substituents. Among the C1-C22 alcanols, C4-C18 alcanols are preferred, particularly C6-C18 alcanols. Among the C3-C22 branched alcohols, C8-C22 alcohols are preferred. The fatty acid esters obtained from C1-C22 branched primary alcohols, preferably C6 to C18, are called wax-esters in this invention. The term wax-esters generally covers esters of fatty acids and fatty alcohols that are solid at room temperature. By extension, the term is also used to cover any fatty acid or fatty alcohol esters that are solid or liquid at room temperature obtained in accordance with this invention. By varying the length of the saturated alcohol used, it is possible to obtain wax-esters from vegetable oils that are liquid at 20xc2x0 C.
According to a preferred embodiment of the invention, the alcohol is chosen from among 1-hexanol, 1-octanol, 1-decanol, 1-dodecanol, 1-tetradecanol, 1-hexadecanol, 1-octadecanol, hexyldecanol or oleic alcohol.
Advantageously, about 30% to about 150% by weight of alcohol with respect to fatty material weight is used in step a). At the end of the interesterification reaction, content in residual alcohol is generally between about 20% by weight and about 35% by weight with respect to the weight of starting alcohol used.
The catalyst used to trigger the interesterification reaction is preferably an alkaline base, an alkaline metal alcoholate, an alkaline metal or a strong acid.
Advantageously, the catalyst is chosen from among soda, sodium methylate, metallic sodium or 4-toluene sulphonic acid.
The interesterification reaction is generally carried out for about 0.5 hour to about 10 hours, with stirring under an inert atmosphere, for example nitrogen, and at a temperature at least equal to about 100xc2x0 C. and at most equal to about 200xc2x0 C.
Advantageously, elimination of the catalyst in step b), when the catalyst is of the alkaline type, is carried out with an excess of about 500%, with respect to the stoichiometric amount, of a strong acid such as sulphuric acid or hydrochloric acid in aqueous solution of at least N and at most 5N, necessary for neutralisation of the alkaline catalyst, by stirring at room temperature for at least 30 minutes and at most about 1 hour. The catalyst neutralisation process is followed by washing with water, with each washing carried out under stirring at a temperature between about 80xc2x0 C. and about 100xc2x0 C., using an amount of water equal to at least 10% by weight and at most 20% by weight of the product weight to be washed. Between two and four washes are generally needed to attain neutrality. When the catalyst is a strong acid, elimination of this acid is advantageously carried out by straightforward washing with water. To carry out these washing processes at room temperature between about 80xc2x0 C. and about 100xc2x0 C. with stirring, an amount of water is used equal to at least 10% by weight and at most 20% by weight of product weight to be washed. As many washes as necessary are carried out until the washing water has a neutral pH.
Distillation of the residual alcohol in the product neutralised in step c) is carried out under absolute pressure of about 10 to 100 Pascal, at a temperature equal to at least 65xc2x0 C. and at most about 230xc2x0 C., for a period of time generally equal, at most, to about 4 hours and preferably equal to about 2 hours. Advantageously, said distillation process is carried out in the presence of a quantity of bleaching agent, for example activated charcoal, equal to at least about 0.1% by weight and at most about 1% by weight of the product to be distilled. After cooling down completely, the bleaching agent is generally separated from the distillation residue by straightforward filtration.
The frigelisation process is carried out in step d1) by stirring the bleached distillate at a temperature between about 10xc2x0 C. and about 14xc2x0 C. for a period of time generally at least equal to about 1 hour and at most to about 4 hours after which the frigelised product is filtered.
The frigelisation temperature can be reduced but this carries a risk in that part of the wax-esters according to the invention might be crystallized and eliminated with the crystallized residual glycerides.
According to one embodiment of the invention, the product (residue) recovered after distillation of the residual alcohol is hydrogenated in a reactor under hydrogen pressure of about 1 to about 20 bar, in the presence of a catalyst such as a nickel- or palladium-based catalyst, at a temperature equal to at least 100xc2x0 C. and at most about 220xc2x0 C., for a period of time equal to at least about 2 hours and at most about 8 hours. Under these conditions, all unsaturated parts of the acid and alcohol carbon chain (if it is unsaturated) are hydrogenated with the hydrogenated product having an iodine number of less than 1. The catalyst is separated by straightforward filtration on paper.
Advantageously, the product obtained in step d1) or d2) has a wax-ester content (expressed as a percentage with respect to the weight of product obtained) between about 55% by weight and about 95% by weight, preferably between about 66% and about 90% by weight, and more especially between 70% by weight and about 80% by weight.
According to another aspect, the invention relates to a wax-ester based non-oily emollient which can be obtained by the process described above. This emollient has the following characteristics:
liquid, solid or fat-like consistency at 20xc2x0 C.,
perfectly suitable for the epidermis,
dry and silky to the touch,
easy to spread,
penetrates the epidermis quickly
has dermatological properties identical to those of the starting oil.
Preferably, the non-oily emollient according to the invention consists of a mixture of:
66 to 95% by weight of wax-esters,
0.1 to 12% by weight of triglycerides,
3 to 20% by weight of diglycerides, and
1.5 to 10% by weight of monoglycerides (as proportions of these four components total 100%, to the nearest insaponifiable matter, the latter generally represents about 0.1 to 1.5% by weight).